bsd-comp.c

Unix/Linux NAPT协议解析源码

/* Because this code is derived from the 4.3BSD compress source:
 *
 *
 * Copyright (c) 1985, 1986 The Regents of the University of California.
 * All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * James A. Woods, derived from original work by Spencer Thomas
 * and Joseph Orost.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * This version is for use with mbufs on BSD-derived systems.
 *
 * $Id: bsd-comp.c,v 1.11 1995/07/04 03:35:11 paulus Exp $
 */

#include <slirp.h>

#define M_INC_COMP 4096	/* XXXXX */

#include <ppp/ppp-comp.h>

#if DO_BSD_COMPRESS
/*
 * PPP "BSD compress" compression
 *  The differences between this compression and the classic BSD LZW
 *  source are obvious from the requirement that the classic code worked
 *  with files while this handles arbitrarily long streams that
 *  are broken into packets.  They are:
 *
 *	When the code size expands, a block of junk is not emitted by
 *	    the compressor and not expected by the decompressor.
 *
 *	New codes are not necessarily assigned every time an old
 *	    code is output by the compressor.  This is because a packet
 *	    end forces a code to be emitted, but does not imply that a
 *	    new sequence has been seen.
 *
 *	The compression ratio is checked at the first end of a packet
 *	    after the appropriate gap.	Besides simplifying and speeding
 *	    things up, this makes it more likely that the transmitter
 *	    and receiver will agree when the dictionary is cleared when
 *	    compression is not going well.
 */

#define BSD_OVHD	2		/* BSD compress overhead/packet */
#define BSD_INIT_BITS	BSD_MIN_BITS

static void	*bsd_comp_alloc __P((u_char *options, int opt_len));
static void	*bsd_decomp_alloc __P((u_char *options, int opt_len));
static void	bsd_free __P((void *state));
static int	bsd_comp_init __P((void *state, u_char *options, int opt_len,
				   int unit, int hdrlen, int debug));
static int	bsd_decomp_init __P((void *state, u_char *options, int opt_len,
				     int unit, int hdrlen, int mru, int debug));
static int	bsd_compress __P((void *state, struct mbuf **mret,
				  struct mbuf *mp, int slen, int maxolen, int proto));
static void	bsd_incomp __P((void *state, struct mbuf *dmsg, int proto));
static int	bsd_decompress __P((void *state, struct mbuf *cmp,
				    struct mbuf **dmpp));
static void	bsd_reset __P((void *state));
static void	bsd_comp_stats __P((void *state, struct compstat *stats));

#include "bsd-comp.h"

/*
 * the next two codes should not be changed lightly, as they must not
 * lie within the contiguous general code space.
 */
#define CLEAR	256			/* table clear output code */
#define FIRST	257			/* first free entry */
#define LAST	255

#define MAXCODE(b)	((1 << (b)) - 1)
#define BADCODEM1	MAXCODE(BSD_MAX_BITS)

#define BSD_HASH(prefix,suffix,hshift)	((((u_int32_t)(suffix)) << (hshift)) \
					 ^ (u_int32_t)(prefix))
#define BSD_KEY(prefix,suffix)		((((u_int32_t)(suffix)) << 16) \
					 + (u_int32_t)(prefix))

#define CHECK_GAP	10000		/* Ratio check interval */

#define RATIO_SCALE_LOG	8
#define RATIO_SCALE	(1<<RATIO_SCALE_LOG)
#define RATIO_MAX	(0x7fffffff>>RATIO_SCALE_LOG)

/*
 * Procedures exported to if_ppp.c.
 */
struct compressor ppp_bsd_compress = {
	CI_BSD_COMPRESS,            /* compress_proto */
	bsd_comp_alloc,             /* comp_alloc */
	bsd_free,                   /* comp_free */
	bsd_comp_init,              /* comp_init */
	bsd_reset,                  /* comp_reset */
	bsd_compress,               /* compress */
	bsd_comp_stats,             /* comp_stat */
	bsd_decomp_alloc,           /* decomp_alloc */
	bsd_free,                   /* decomp_free */
	bsd_decomp_init,            /* decomp_init */
	bsd_reset,                  /* decomp_reset */
	bsd_decompress,             /* decompress */
	bsd_incomp,                 /* incomp */
	bsd_comp_stats,             /* decomp_stat */
};


/*
 * clear the dictionary
 */
static void
bsd_clear(db)
    struct bsd_db *db;
{
    db->clear_count++;
    db->max_ent = FIRST-1;
    db->n_bits = BSD_INIT_BITS;
    db->ratio = 0;
    db->bytes_out = 0;
    db->in_count = 0;
    db->incomp_count = 0;
    db->checkpoint = CHECK_GAP;
}

/*
 * If the dictionary is full, then see if it is time to reset it.
 *
 * Compute the compression ratio using fixed-point arithmetic
 * with 8 fractional bits.
 *
 * Since we have an infinite stream instead of a single file,
 * watch only the local compression ratio.
 *
 * Since both peers must reset the dictionary at the same time even in
 * the absence of CLEAR codes (while packets are incompressible), they
 * must compute the same ratio.
 */
static int				/* 1=output CLEAR */
bsd_check(db)
    struct bsd_db *db;
{
    u_int new_ratio;

    if (db->in_count >= db->checkpoint) {
	/* age the ratio by limiting the size of the counts */
	if (db->in_count >= RATIO_MAX
	    || db->bytes_out >= RATIO_MAX) {
	    db->in_count -= db->in_count/4;
	    db->bytes_out -= db->bytes_out/4;
	}

	db->checkpoint = db->in_count + CHECK_GAP;

	if (db->max_ent >= db->maxmaxcode) {
	    /* Reset the dictionary only if the ratio is worse,
	     * or if it looks as if it has been poisoned
	     * by incompressible data.
	     *
	     * This does not overflow, because
	     *	db->in_count <= RATIO_MAX.
	     */
	    new_ratio = db->in_count << RATIO_SCALE_LOG;
	    if (db->bytes_out != 0)
		new_ratio /= db->bytes_out;

	    if (new_ratio < db->ratio || new_ratio < 1 * RATIO_SCALE) {
		bsd_clear(db);
		return 1;
	    }
	    db->ratio = new_ratio;
	}
    }
    return 0;
}

/*
 * Return statistics.
 */
static void
bsd_comp_stats(state, stats)
    void *state;
    struct compstat *stats;
{
    struct bsd_db *db = (struct bsd_db *) state;
    u_int out;

    stats->unc_bytes = db->uncomp_bytes;
    stats->unc_packets = db->uncomp_count;
    stats->comp_bytes = db->comp_bytes;
    stats->comp_packets = db->comp_count;
    stats->inc_bytes = db->incomp_bytes;
    stats->inc_packets = db->incomp_count;
    stats->ratio = db->in_count;
    out = db->bytes_out;
    if (stats->ratio <= 0x7fffff)
	stats->ratio <<= 8;
    else
	out >>= 8;
    if (out != 0)
	stats->ratio /= out;
}

/*
 * Reset state, as on a CCP ResetReq.
 */
static void
bsd_reset(state)
    void *state;
{
    struct bsd_db *db = (struct bsd_db *) state;

    db->seqno = 0;
    bsd_clear(db);
    db->clear_count = 0;
}

/*
 * Allocate space for a (de) compressor.
 */
static void *
bsd_alloc(options, opt_len, decomp)
    u_char *options;
    int opt_len, decomp;
{
    int bits;
    u_int newlen, hsize, hshift, maxmaxcode;
    struct bsd_db *db;

    if (opt_len != CILEN_BSD_COMPRESS || options[0] != CI_BSD_COMPRESS
	|| options[1] != CILEN_BSD_COMPRESS
	|| BSD_VERSION(options[2]) != BSD_CURRENT_VERSION)
	return NULL;
    bits = BSD_NBITS(options[2]);
    switch (bits) {
    case 9:			/* needs 82152 for both directions */
    case 10:			/* needs 84144 */
    case 11:			/* needs 88240 */
    case 12:			/* needs 96432 */
	hsize = 5003;
	hshift = 4;
	break;
    case 13:			/* needs 176784 */
	hsize = 9001;
	hshift = 5;
	break;
    case 14:			/* needs 353744 */
	hsize = 18013;
	hshift = 6;
	break;
    case 15:			/* needs 691440 */
	hsize = 35023;
	hshift = 7;
	break;
    case 16:			/* needs 1366160--far too much, */
	/* hsize = 69001; */	/* and 69001 is too big for cptr */
	/* hshift = 8; */	/* in struct bsd_db */
	/* break; */
    default:
	return NULL;
    }

    maxmaxcode = MAXCODE(bits);
    newlen = sizeof(*db) + (hsize-1) * (sizeof(db->dict[0]));
    db = (struct bsd_db *)malloc(newlen);
    if (!db)
	return NULL;
    memset(db, 0, sizeof(*db) - sizeof(db->dict));

    if (!decomp) {
	db->lens = NULL;
    } else {
	db->lens = (u_short *)malloc((maxmaxcode+1) * sizeof(db->lens[0]));
	if (!db->lens) {
	    free(db);
	    return NULL;
	}
    }

    db->totlen = newlen;
    db->hsize = hsize;
    db->hshift = hshift;
    db->maxmaxcode = maxmaxcode;
    db->maxbits = bits;

    return (void *) db;
}

static void
bsd_free(state)
    void *state;
{
    struct bsd_db *db = (struct bsd_db *) state;

    if (db->lens)
	free(db->lens);
    free(db);
}

static void *
bsd_comp_alloc(options, opt_len)
    u_char *options;
    int opt_len;
{
    return bsd_alloc(options, opt_len, 0);
}

static void *
bsd_decomp_alloc(options, opt_len)
    u_char *options;
    int opt_len;
{
    return bsd_alloc(options, opt_len, 1);
}

/*
 * Initialize the database.
 */
static int
bsd_init(db, options, opt_len, unit, hdrlen, mru, debug, decomp)
    struct bsd_db *db;
    u_char *options;
    int opt_len, unit, hdrlen, mru, debug, decomp;
{
    int i;

    if (opt_len != CILEN_BSD_COMPRESS || options[0] != CI_BSD_COMPRESS
	|| options[1] != CILEN_BSD_COMPRESS
	|| BSD_VERSION(options[2]) != BSD_CURRENT_VERSION
	|| BSD_NBITS(options[2]) != db->maxbits
	|| decomp && db->lens == NULL)
	return 0;

    if (decomp) {
	i = LAST+1;
	while (i != 0)
	    db->lens[--i] = 1;
    }
    i = db->hsize;
    while (i != 0) {
	db->dict[--i].codem1 = BADCODEM1;
	db->dict[i].cptr = 0;
    }

    db->unit = unit;
    db->hdrlen = hdrlen;
    db->mru = mru;
#ifndef DEBUG
    if (debug)
#endif
	db->debug = 1;

    bsd_reset(db);

    return 1;
}

static int
bsd_comp_init(state, options, opt_len, unit, hdrlen, debug)
    void *state;
    u_char *options;
    int opt_len, unit, hdrlen, debug;
{
    return bsd_init((struct bsd_db *) state, options, opt_len,
		    unit, hdrlen, 0, debug, 0);
}

static int
bsd_decomp_init(state, options, opt_len, unit, hdrlen, mru, debug)
    void *state;
    u_char *options;
    int opt_len, unit, hdrlen, mru, debug;
{
    return bsd_init((struct bsd_db *) state, options, opt_len,
		    unit, hdrlen, mru, debug, 1);
}


/*
 * compress a packet
 *	One change from the BSD compress command is that when the
 *	code size expands, we do not output a bunch of padding.
 */
int					/* new slen */
bsd_compress(state, mret, mp, slen, maxolen, proto)
    void *state;
    struct mbuf **mret;		/* return compressed mbuf chain here */
    struct mbuf *mp;		/* from here */
    int slen;			/* uncompressed length */
    int maxolen;		/* max compressed length */
    int proto;
{
    struct bsd_db *db = (struct bsd_db *) state;
    int hshift = db->hshift;
    u_int max_ent = db->max_ent;
    u_int n_bits = db->n_bits;
    u_int bitno = 32;
    u_int32_t accm = 0, fcode;
    struct bsd_dict *dictp;
    u_char c;
    int hval, disp, ent, ilen;
    struct mbuf *np;
    u_char *rptr, *wptr;
    u_char *cp_end;
    int olen;
    struct mbuf *m, **mnp;

/*
 * XXXXX MUST check for end-of-buffer, and if it happens, bail!
 * (more efficient than mallocing then realising it's too big etc.)
 */
#define PUTBYTE(v) {					\
    ++olen;						\
    if (wptr) {						\
        *wptr++ = (v);					\
	if (wptr >= cp_end) {				\
	    m_inc(m, M_INC_COMP);			\
	    wptr = mtod(m, u_char *);			\
	    cp_end = m->m_ext + m->m_size;		\
	}						\
    }							\
}

#define OUTPUT(ent) {					\
    bitno -= n_bits;					\
    accm |= ((ent) << bitno);				\
    do {						\
	PUTBYTE(accm >> 24);				\
	accm <<= 8;					\
	bitno += 8;					\
    } while (bitno <= 24);				\
}
    /*
     * If the protocol is not in the range we're interested in,
     * just return without compressing the packet.  If it is,
     * the protocol becomes the first byte to compress.
     */
    rptr = mtod(mp, u_char *);
    ent = proto;
    if (ent < 0x21 || ent > 0xf9) {
        *mret = NULL;
	return slen;
    }
    
    /* Don't generate compressed packets which are larger than
       the uncompressed packet. */
    if (maxolen > slen)
	maxolen = slen;

    /* Allocate one mbuf to start with. */
    m = m_get();
    m->m_data += if_maxlinkhdr;
    *mret = m;
    if (m != NULL) {
	m->m_data += db->hdrlen;
	wptr = mtod(m, u_char *);
	cp_end = wptr + M_TRAILINGSPACE(m);
    } else
	wptr = cp_end = NULL;

    /*
     * install the 2-byte packet sequence number.
     */
    if (wptr) {
	*wptr++ = db->seqno >> 8;
	*wptr++ = db->seqno;